The present invention relates to a porous sintered body of a calcium phosphate-based ceramic and a method for producing the porous sintered body. The porous sintered body is useful as a carrier for cultivation of cells or biological tissues and as a biocompatible artificial material suitable for filling a defective part of a bone, etc., and further, the porous sintered body is excellent in mechanical strength and machinability to be usable as a filler for a liquid chromatography, a catalyst-carrier, an electric or electronic material, a nuclear reactor material, a ceramic heating element, etc.
Calcium phosphate-based ceramic such as hydroxyapatite has an excellent biocompatibility to have been used as a carrier for cultivation of cells or biological tissues, a biomaterial such as an artificial dental root and a bone-reinforcing material, etc. It is preferred that the calcium phosphate-based ceramic is compact from the viewpoint of a mechanical strength. However, it is preferred that the calcium phosphate-based ceramic is porous, thus, that a porosity of the calcium phosphate-based ceramic is as high as possible from the viewpoint of a biocompatibility. Therefore, various methods have been proposed to produce the porous calcium phosphate-based ceramic, for example, frother methods, pyrolytic resin beads methods, spongy resin impregnation methods, water-soluble high molecular compound gelation methods, etc.
In the frother methods, to a slurry of hydroxyapatite, etc. is added a frother such as hydrogen peroxide water to froth the slurry, thereby increasing the porosity of the calcium phosphate-based ceramic. However, there is a limit in the porosity, and it is difficult to control an average pore-diameter and the porosity regularly in every lot in the frother methods. In the pyrolytic resin beads methods, pyrolytic resin beads are added to a slurry of hydroxyapatite, etc., mixed and formed therewith, and the resultant formed body is heated to burn down the pyrolytic resin beads, thereby producing the porous calcium phosphate-based ceramic. However, the pyrolytic resin beads methods are disadvantageous in that the formed body is often warped or cracked because the pyrolytic resin beads are not constricted in a drying process. Further, a large quantity of the pyrolytic resin beads is used in the methods, whereby long period of time is required in sintering and a large quantity of carbon dioxide gas is unavoidably provided. Furthermore, the porosity of the porous calcium phosphate-based ceramic produced by the pyrolytic resin beads methods is approximately equal to but no more than 50%. The spongy resin impregnation methods have been widely used to produce the porous calcium phosphate-based ceramic, the porosity of the porous calcium phosphate-based ceramic produced thereby depends on a porosity of the spongy resin to be approximately 75% at most. Therefore, the porous calcium phosphate-based ceramic having desired minute pores cannot be produced by the spongy resin impregnation methods.
In the water-soluble high molecular compound gelation methods, a slurry comprising a ceramic and a water-soluble high molecular compound is stirred to froth the slurry, the frothed slurry is heated for gelation, and the resultant gel containing air babbles is dried to provide a porous ceramic as disclosed in Japanese Patent No. 3058174. The porous ceramic produced by a method described in Japanese Patent No. 3058174 has spherical macro-pores resulting from the air babbles having a pore diameter of 20 to 2000 μm and three dimensional passing-through pores formed by gaps between spherical secondary particles composed of an aggregate of primary particles of the ceramic raw material. However, under a circumstances where the porous calcium phosphate-based ceramic have been required to be further improved in the biocompatibility, there has been increasing need for the porous calcium phosphate-based ceramic having a further high porosity.